The present invention relates to production of high purity extra fine and fine powders of transition metals such as Fe, Co, Ni, Cu, Zn, V, W, Mo, etc., which can be used for manufacturing of various articles by powder metallurgy technology or other technology involving shaping of a green product and its subsequent sintering. In the present invention the fine powder is the powder with particle size 10-45 micron and the extra fine powder is that one which has particle size 1-5 microns.
One of the requirements which the metal powder should meet is the uniformity of the powder size and its purity from oxygen and carbon. Conventionally metal powders satisfying these requirements have been prepared by various processes involving direct reduction of metal oxides within a stream of hydrogen at temperatures about 1100.degree. C. The disadvantage of the processes based on direct reduction is associated with the necessity to prepare corresponding metal oxide for example from corresponding metal oxalate or carbonate. This procedure is complicated and energy consuming. Moreover, obtaining of metal oxides from carbonates or oxalates is associated with inclusion of carbon in the final powder, which might affect the properties of a product manufactured from such powder.
Some metal powders, such like Ni, Zn and Cu powders are prepared by hydro-metallurgical treatment of the appropriate raw material to prepare solution of the metal salt with subsequent electrolysis thereof. This technology also requires high consumption of electrical energy.
Some metal powders, such as Fe, Co, Ni, Cu, etc., can be obtained by the atomization process in which ingots of those metals are melted and sprayed. This process requires exceptionally high energy consumption and since it does not involve any chemical transformation the purity of the resulting powder can not be better then that of the starting material.
Fine powders of transition, metals can be produced by mechanical crushing of metal ingots within a stream of hydrogen or an inert gas. Unfortunately a great deal of mechanical energy is required to produce metal powder with particle size slightly less then 40 .mu.m, while an extra-fine powder with particle size of 1 .mu.m can not be manufactured at all by any mechanical means.
There is known also to use reducing of metal halides in a hydrogen plasma or H.sub.2 /F.sub.2 flame for producing of extra-fine powders of V, W and Mo. Unfortunately this process is technologically complicated, requires dedicated machinery and is associated with high energy expenditures.
Fine powders of Cu, Ni and Co are produced by hydrogen reducing of aqueous solution of their ions, however this method requires high temperature and pressure and therefore can be carried out only within dedicated equipment having complicated construction.
Extra-fine metal powders can be produced by hydrogen reduction of metal fluorine containing compounds within the hydrogen stream. The shortcoming of this processes is associated with the necessity in an external means for establishing the hydrogen stream. Besides since the process is carried out within a stream and not within a stationary atmosphere there exists the possibility for contamination of the surrounding environment by harmful gaseous products formed during the reduction process.
Therefore it can be seen that despite the existence of various methods for manufacturing of metallic powder there is still felt a need for a new and improved method which will sufficiently reduce or overcome the above mentioned drawbacks of the prior methods.